The coating of large area substrates, such as architectural glass, automobile windshields and the like, has been accomplished for some time by a sputtering process that includes the use of a planar magnetron. Such coatings include multilayer solar control coatings that are widely used on commercial building windows. Typical multilayer solar control coatings comprise metal-dielectric film stacks of three, five, or seven layers which can be used for low emissivity, heat mirror (solar control), or heated (defroster) applications. Zinc oxide, tin oxide, indium oxide, or mixtures thereof are common dielectric materials used in such films. See Gillery, U.S. Pat. No. 4,806,221, issued Feb. 21, 1989; Belkind et al., U.S. Pat. No. 4,769,291, issued Sep. 6, 1988; Gillery, U.S. Pat. No. 4,610,771; issued Sep. 9, 1986; Dietrich et al., U.S. Pat. No. 4,548,691, issued Oct. 22, 1985; Siewert et al., U.S. Pat. No. 4,466,940, issued Aug. 21, 1984; Grubb et al., U.S. Pat. No. 4,022,947, issued May 10, 1977; and Donley, U.S. Pat. No. 3,978,272, issued Aug. 31, 1976.
More recently, rotating cylindrical magnetrons have been employed for depositing the dielectric layers. In some rotating cylindrical magnetrons the cathode target assembly is in the form of a elongated, solid tube manufactured from target material. However, hitherto self-supporting solid targets can only be manufactured from relatively hard metals or alloys with high melting points such as stainless steel, copper, and titanium. In other cylindrical magnetrons, the target assembly comprises a non-magnetic support tube that carries a layer of target material applied to its outer surface that is to be sputtered. Plasma and liquid metal spray techniques are often employed to apply the target material onto the support tube. In some other cases, metal target material is cast on a stainless steel support. For metallic target materials, the metal ions sputtered therefrom can react with reactive gases such as oxygen to form a metal oxide that is deposited onto a particular substrate. However, cathode targets so fabricated are often inefficient and inadequate. One problem is that poor bonding between the support tube and the target material leads to poor thermal contact and inadequate cooling. Moreover, differences in thermal expansion between the support and target materials also contribute to target deterioration. These problems are particularly acute for soft target materials like zinc.